The purpose of the study is to determine in subjects with Type 1 & 2 diabetes mellitus currently receiving insulin therapy: 1) whether glycemic control can be achieved at least as effectively with an insulin regimen involving pre-meal inhaled insulin plus a single bedtime Ultralente injection as with a conventional subcutaneous insulin regimen involving 2-3 injections per day; and 2) the toleration and safety of inhaled insulin therapy and its effects, if any, on measures of pulmonary function.